Changing and correcting existing genes is not creating new genes that produce new proteins. It is not the topic at hand. It is not possible to make a living complex multi-cell organism produce entirely new enzymes that would destroy certain harmful substances. It would be possible to inject those enzymes, though that would be a lifelong therapy (that's how diabetes gets treated, for instance). Such treatments are very expensive and cannot be done on the scale you proposed (such as giving the treatment to everyone for certain effects such as immunity against harmful substances).
Referring to a gene that codes a protein incorrectly as corrupted is not incorrect? It is a disadvantage and bad mutation, if you want to put it that way. The terminology is understood so it is not necessary to nitpick it.
Genetherapy has been incredibly unsuccessful, as I said.
Most textbooks on the subject are going to say exactly that. Of course there are hopes that gene therapy will become a good thing in the future, just not on the scale you proposed.
Here is a source, if you desire one. http://learn.genetics.utah.edu/conte...apy/gtsuccess/

This thread is not about gene therapy anyway. It is about gmo. They are entirely different. It is not possible to enhance a complex multi-cell organism with new genes.
It is not possible to add new genes to a genome because it requires heavy manipulation that literally involves cutting existing genes and adding new ones, to put it simply.
That is done with individual cells. After the procedure they have to undergo a process of selection which kills off cells where genes have been added incorrectly. It is not possible to add genes to organisms with a 100% success rate. That is because the process involves a lot of chance. There are many possible outcomes which are not desirable. That is why after that procedure a procedure of selection has to take place.
Here is a simple graphic that explains it in laymen terms:
http://www.littletree.com.au/images/dna3.jpg
There are gmo cows and sheep that produce certain human proteins for medical purposes, such as insulin. There the gametes are manipulated, not the whole living organism. Note that the graphic I provided is about e. coli, which are bacteria. Their cells are by far not as complex as those of cows.


I have upcoming exams about that exact subject. If you desire so I can give you some keywords you can look up in order to educate yourself.
What you provided so far does not convince me you know anything about the subject.